Various electro-optical systems have been developed for reading optical indicia, such as bar codes. A bar code is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths, the bars and spaces having differing light reflecting characteristics. The pattern of the bars and spaces encode information. Bar code may be one dimensional (e.g., UPC bar code) or two dimensional (e.g., DataMatrix bar code). Systems that read, that is, image and decode bar codes employing imaging camera systems are typically referred to as imaging-based bar code readers or bar code scanners.
Imaging-based bar code readers may be portable or stationary. A portable bar code reader is one that is adapted to be held in a user's hand and moved with respect to a target indicia, such as a target bar code, to be read, that is, imaged and decoded. Stationary bar code readers are mounted in a fixed position, for example, relative to a point-of-sales counter. The bar code reader is installed behind one or more transparent windows in a housing which may be integrated into the counter. Target objects, e.g., a product package that includes a target bar code, are presented to one of the one or more transparent windows and thereby pass within a field of view of the stationary bar code readers. The bar code reader typically provides an audible and/or visual signal to indicate the target bar code has been successfully imaged and decoded.
A typical example where a stationary imaging-based bar code reader would be utilized includes a point of sale counter/cash register where customers pay for their purchases. The reader is typically enclosed in a housing that is integral to the counter and normally includes a vertically oriented transparent window and/or a horizontally oriented transparent window, either of which may be used for reading the target bar code affixed to the target object, i.e., the product or product packaging for the product having the target bar code imprinted or affixed to it. The sales person (or customer in the case of self-service check out) sequentially presents each target object's bar code either to the vertically oriented window or the horizontally oriented window, whichever is more convenient given the specific size and shape of the target object and the position of the bar code on the target object.
A stationary imaging-based bar code reader that comprises a plurality of imaging cameras systems is sometimes referred to as a bioptic or multicamera imaging-based scanner or bar code reader. In a multicamera imaging reader, each camera system typically is positioned behind one of the plurality of transparent windows such that it has a different field of view from every other camera system. While the fields of view may overlap to some degree, the effective or total field of view of the reader is increased by adding additional camera systems. Hence, the desirability of multicamera readers as compared to signal camera readers which have a smaller effective field of view and require presentation of a target bar code to the reader in a very limited orientation to obtain a successful, decodable image, that is, an image of the target bar code that is decodable.
The camera systems of a multicamera imaging reader may be positioned within the housing and with respect to the transparent windows such that when a target object is presented to the housing for reading the target bar code on the target object, the target object is imaged by the plurality of imaging camera systems, each camera providing a different image of the target object. For example, one camera system may be positioned to image a top view of the target object, another camera may image a bottom view of the target object, yet another camera may image a first side of the target object. Depending on the position of the camera systems and the size of the target object being imaged, it is possible for a small target object, e.g., a small six sided box containing a bottle of aspirin, that all six sides of the target object may be imaged. Thus, it is also clear that increasing the number of camera assemblies increases the ability to image a target bar code on a target object and provides greater flexibility as to how the target object may be oriented or presented to the housing or the transparent windows while still achieving at least one decodable image.
One problem with multicamera imaging-based bar code readers is that they require a very high bandwidth interface to the cameras for image acquisition. For example, a six camera imaging system running at 26 MHz (megahertz) requires a throughput of 156 Mbytes/second. This is the equivalent of six cameras running at 60 frames per second each at 752×480 pixel resolution. This throughput of 156 Mbytes/second places tremendous demand on the bus interface of the image processing system.
Another problem facing designers of multicamera imaging readers is the number of electrical connections to the image processing system. A camera requires at minimum two control lines, three synchronization lines, and typically eight data lines for transmitting data bits. Thus, for a six camera system, this can result in up to 13×6=78 electrical connections to the image processing system. The interface between the cameras and the image processing system is typically controlled by an ASIC (application specific integrated circuit). The greater the number of electrical connections to the image processing system, the greater the cost of the ASIC that is used to implement the interface between the cameras and the image processing system.
With the trend of increasing the number of camera assemblies in multicamera imaging bar code reader to increase the effective field of view and ability to image target bar codes regardless of their presentation orientation, the problems of high bandwidth interface and the number of electrical connections to the image processing system will only become more problematic in the future.
What is needed is a multicamera imaging-based bar code reader and a method of operating a multicamera imaging-based bar code reader that reduces the required interface bandwidth of the bus interface of the imaging processing system and/or reduces the number of electrical connections to the image processing system.